28029 Parallax Inc, 28029 Datasheet - Page 79

• Manufacturer Part Number: 28029
• Description: KIT PARTS SMART SENSORS W/TEXT
• Manufacturer: Parallax Inc

Specifications of 28029

• Accessory Type: Parts Kit
• Product: Microcontroller Accessories
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• For Use With/related Products: BASIC Stamp® or Javelin Modules
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant, Contains lead / RoHS non-compliant
• Other names: 28029PAR

Chapter 3: Tilt with the Memsic Accelerometer · Page 67
THE MX2125 ACCELEROMETER – HOW IT WORKS
The MX2125’s design is amazingly simple. It has a chamber of gas with a heating
element in the center and four temperature sensors around its edge. Just as hot air rises
and cooler air sinks, the same applies to hot and cool gasses.
If you hold the
accelerometer still, all it senses is gravity, and tilting it gives us an example of how it
senses static acceleration. When you hold the accelerometer level, the hot gas pocket
rises to the top-center of the accelerometer’s chamber, and all the sensors will measure
the same temperature. Depending on how you tilt the accelerometer, the hot gas will
collect closer to one or maybe two of the temperature sensors.
Figure 3-2: The Accelerometer’s Heated Gas Pocket
By comparing the sensor temperatures, both static acceleration (gravity and tilt) and
dynamic acceleration (like taking a ride in a car) can be detected. If you were to take the
accelerometer for a car ride, the hotter and cooler gasses would slosh around in the
chamber in a manner similar to a container half-full of water, and the sensors would
detect this.
In most situations, making sense out of these measurements is a simple task thanks to the
electronics inside the MX2125. The MX2125 converts the temperature measurements
into signals (pulse durations) that are easy for the BASIC Stamp microcontroller to
measure and decipher.